Oosthuizen is 13-under-par midway through his third round. Bad weather pushed play back and just 12 players completed third-round play Saturday.
Oosthuizen birdied No. 10 for the third consecutive round before play was halted Saturday. He'll finish eight holes of the third round Sunday before the final round begins.
Stephan Gallacher is 3-under after 11 holes of the third round and is 12-under for the tournament. Rafael Cabrera-Bello, who got in 13 third-round holes Saturday; David Lipsky, with seven holes left in the round; and Danny Willett, through 12 holes in the third round, are tied for third at 10-under.
Oosthuizen opened the day by finishing six holes of his second round, which was suspended Friday because of lightning. He was 10-under after a bogey-free second round and is 3-under, with a bogey at the sixth hole, after 10 holes in the third.
Gallacher, who has just one bogey so far in the tournament, had two birdies and five pars in completing his second round Saturday and had three birdies over No. 2-4 in the third round.